"Life is what you make it" is a claim about responsibility, not a claim about fairness. Strip away the poster-and-mug version of it and it says something...

"Life is what you make it" is a claim about responsibility, not a claim about fairness. Strip away the poster-and-mug version of it and it says something fairly narrow: the raw material you are handed (your family, your health, the economy you graduated into, the accidents that happen to you) is not the whole story. What you do with that material, the choices, habits, and effort you put on top of it, shapes the outcome as much as the material itself does.
It is not saying that circumstances do not matter. It is saying they are not the only variable. Two people can start from similar positions and end up somewhere different because of what each of them did next. That is the entire claim. Everything else people load onto it, about attitude, about destiny, about willpower, is decoration added afterward.
Both versions get searched, and they are not quite interchangeable.
"Life is what you make it" is the stronger, more active version. It puts the emphasis on construction: you are building something, and the result is largely a product of your own doing. It leans toward agency and effort.
"Life is what you make of it" shifts the emphasis slightly toward interpretation and use. "Make of" is closer to "make sense of" or "make use of", the way you might make something of a difficult year, a bad hand, or an unplanned move. It allows more room for the idea that you did not choose the situation, only how you responded to it and what you extracted from it.
The difference is small but it matters if you are trying to use the phrase precisely. "Make it" says you are the author. "Make of it" says you are the reader, working out what a chapter you didn't write means for what comes next. Most people use them as if they mean exactly the same thing, and in casual conversation that is fine. If you are quoting it deliberately, pick the one that matches what you are actually trying to say.
Here is the honest answer, which is less satisfying than most pages on this topic will give you: nobody reliably knows who said it first, and you should be suspicious of any page that names a single confident author.
The phrase has been attributed online to a long list of people, and those attributions circulate with total confidence and almost no sourcing behind them. That pattern, a saying with no clear origin acquiring a famous name because it sounds like something that person would say, is extremely common with proverbial sayings. Once one site attributes a quote to someone, it gets copied to the next, and repetition starts to look like evidence when it is not.
What can be said honestly is that the underlying sentiment, that a person's effort and choices shape their outcome as much as their starting conditions do, shows up in much older proverb traditions, expressed in different words, long before this exact wording existed. That is typical of how proverbs work. They tend to accumulate a fixed, quotable phrasing over time, usually without a single identifiable author, rather than being coined once by one person and then spreading.
If you searched for who said this hoping for a name, the accurate answer is that no one has reliably established one. That is not a dodge. It is what the record actually supports, and it is worth more than a confident guess.
The obvious problem with the phrase is that it can slide into blaming people for things they did not cause. Told to someone dealing with a layoff, a health problem, or a family situation they did not choose, "life is what you make it" can sound like an accusation: if things are hard, you must not be trying hard enough.
That version of the phrase is not useful and it is not accurate. Some constraints are real and are not something effort dissolves. A single income supporting a family has less room to maneuver than two. An illness limits what a body can do regardless of attitude. A local job market either has openings or it does not. Pretending otherwise, in either direction, does not help anyone.
Where the phrase earns its keep is at the margin, in the part of a situation that is still within your control even after you have accounted for what isn't. You cannot always control the size of the paycheck. You usually can control what you do with a free Tuesday evening, whether you follow up on the thing you said you would follow up on, and whether you spend an hour of downtime on something that moves you forward or something that does not. The phrase is a decent description of that margin. It is a bad description of everything outside it.
None of this needs to be dramatic to be true. Take a week where the car needs a repair you did not budget for, one kid has a school project due, and you are tired most evenings. You did not choose the car repair. That part is not "what you make it." But you still decide, inside that constraint, whether you call the mechanic Monday or let it slide to Thursday and pay more for the delay. You still decide whether the school project gets fifteen minutes of your attention spread across three nights or gets ignored until the night before. You still decide whether the tired evening goes to sitting with the kids for ten minutes before bed or gets absorbed entirely by the day's leftover stress.
None of those decisions fix the car or the budget. They are also not nothing. Applied honestly, the phrase is not a call to reinvent your circumstances. It is a reminder to notice the small number of choices inside a hard week that are actually yours, and to spend them on purpose instead of by default.
Pick one recurring decision in your week that you have been making on autopilot, something like when you leave for work, whether you check in with one of your kids before the day gets away from you, or how you spend the first twenty minutes after they're in bed. Make that one decision deliberately for the next seven days instead of letting the day decide it for you. That is the whole exercise. It will not change your income or your circumstances. It is the part of the phrase that is actually true.