The Enchiridion by Epictetus translated by William Abbot Oldfather (1928): 29

 The Enchiridion by Epictetus translated by William Abbot Oldfather (1928): 29

Bonus: 

Kind of the opposite of this.

Summary: You sure you wanna do that?

Commentary: 

29: Think about what you'll need to do to achieve your goals. Only take them up if you're willing to do your work, otherwise you're just wasting your time playing.

I'm just going to drop the whole thing in here, because I think it's one of the more interesting ones and worth talking about a little bit.

In each separate thing that you do, consider the matters which come first and those which follow after, and only then approach the thing itself. Otherwise, at the start you will come to it enthusiastically, because you have never reflected upon any of the subsequent steps, but later on, when some difficulties appear, you will give up disgracefully. Do you wish to win an Olympic victory? So do I, by the gods! for it is a fine thing. But consider the matters which come before that, and those which follow after, and only when you have done that, put your hand to the task. You have to submit to discipline, follow a strict diet, give up sweet cakes, train under compulsion, at a fixed hour, in heat or in cold; you must not drink cold water, nor wine just whenever you feel like it; you must have turned yourself over to your trainer precisely as you would to a physician. Then when the contest comes on, you have to “dig in” beside your opponent, and sometimes dislocate your wrist, sprain your ankle, swallow quantities of sand, sometimes take a scourging, and along with all that get beaten. After you have considered all these points, go on into the games, if you still wish to do so; otherwise, you will be turning back like children. Sometimes they play wrestlers, again gladiators, again they blow trumpets, and then act a play. So you too are now an athlete, now a gladiator, then a rhetorician, then a philosopher, yet with your whole soul nothing; but like an ape you imitate whatever you see, and one thing after another strikes your fancy. For you have never gone out after anything with circumspection, nor after you had examined it all over, but you act at haphazard and half-heartedly.

In the same way, when some people have seen a philosopher and have heard someone speaking like Euphrates (though, indeed, who can speak like him?), they wish to be philosophers themselves. Man, consider first the nature of the business, and then learn your own natural ability, if you are able to bear it. Do you wish to be a contender in the pentathlon, or a wrestler? Look to your arms, your thighs, see what your loins are like. For one man has a natural talent for one thing, another for another. Do you suppose that you can eat in the same fashion, drink in the same fashion, give way to impulse and to irritation, just as you do now? You must keep vigils, work hard, abandon your own people, be despised by a paltry slave, be laughed to scorn by those who meet you, in everything get the worst of it, in honour, in office, in court, in every paltry affair. Look these drawbacks over carefully, if you are willing at the price of these things to secure tranquillity, freedom and calm. Otherwise, do not approach philosophy; don’t act like a child—now a philosopher, later on a tax-gatherer, then a rhetorician, then a procurator of Caesar. These things do not go together. You must be one person, either good or bad; you must labour to improve either your own governing principle or externals; you must work hard either on the inner man, or on things outside; that is, play either the rôle of a philosopher or else that of a layman.

So, I see two big things here:

1. Think about what you will actually have to do to achieve your goals. Epictetus's example is winning the Olympics. You'd have to train hard, give up junk food, etc.

Obviously, this is reasonable advice. You can't expect to run a marathon or whatever if you can't even jog to the end of the block, and you probably won't do that if you're downing a 40 and a case of Twinkies a day.

But what I think is more interesting is the contrast with the advice I often see today. What I usually see is "JUST GO DO THE THING! STOP OVERTHINKING! DON'T SPEND A YEAR PREPPING! DO IT!"

The answer is broadly somewhere in the middle (you have to actually try the thing, but you do need to devote effort) but it's just interesting to see something close to the opposite of the "normal" advice.

2. The comparison to kids playing at things.

On the one hand, fair. Kids do rotate through things they want to be pretty quickly. On the other, I think, even as an adult, "playing" and trying stuff has value. How are you supposed to know if you want to try a second career if you never try it? To say nothing of a hobby or whatever. Nothing wrong with an adult trying 5 or 10 things before settling on dedicating themselves to becoming a great chili cooker or whatever.