This is a long one, but a good one.
In every act observe the things which come first, and those which follow it; and so proceed to the act. If you do not, at first you will approach it with alacrity, without having thought of the things which will follow; but afterward, when certain base (ugly) things have shown themselves, you will be ashamed.
As far a "look before you leap" advice goes, I think this is pretty we put together. Before starting out on a new venture, you should fully think through what's involved.
A man wishes to conquer at the Olympic games. I also wish indeed, for it is a fine thing. But observe both the things which come first, and the things which follow; and then begin the act. You must do everything according to rule, eat according to strict orders; abstain from delicacies; exercise yourself as you are bid at appointed times, in heat, in cold; you must not drink cold water, nor wine as you choose. In a word, you must deliver yourself up to the exercise master as you do to the physician, and then proceed to the contest. And sometimes you will strain the hand, put the ankle out of joint, swallow much dust, sometimes be flogged, and after all this be defeated. When you have considered all this, if you still choose, go to the contest: if you do not, you will behave like children, who at one time play at wrestlers, another time as flute players, again as gladiators, then as trumpeters, then as tragic actors: so you also will be at one time an athlete, at another a gladiator, then a rhetorician, then a philosopher, but with your whole soul you will be nothing at all; but like an ape you imitate everything that you see, and one thing after another pleases you. For you have not undertaken anything with consideration, nor have you surveyed it well; but carelessly and with cold desire.
This extended example drives the point home. Don't play at a role: you're not a child. If you decide to do something, do it with full knowledge and commitment.
Thus some who have seen a philosopher and having heard one speak, as Euphrates speaks - and who can speak as he does? They wish to be philosophers themselves also. My man, first of all consider what kind of thing it is: and then examine your own nature, if you are able to sustain the character. Do you wish to be a pentathlete or a wrestler? Look at your arms, your thighs, examine your loins. For different men are formed by nature for different things. Do you think that if you do these things, you can eat in the same manner, drink in the same manner, and in the same manner loathe certain things? You must pass sleepless nights; endure toil; go away from your kinsmen; be despised by a slave; in everything have the inferior part, in honor, in office, in the courts of justice, in every little matter. Consider these things, if you would exchange for them, freedom from passions, liberty, tranquility. If not, take care that, like little children, you be not now a philosopher, then a servant of the publican, then a rhetorician, then a procurator (manager) for Caesar. These things are not consistent. You must be one man, either good or bad. You must either cultivate your own ruling faculty, or external things; you must either exercise your skill on internal things or on external things; that is, you must either maintain the position of a philosopher or that of a common person.
As part of your consideration of the reality of the path ahead of you, consider your suitability to walking walking that path. Epictetus also takes the opportunity to lay out that path of the philosopher; again a warning against pursuing philosophy if you don't have the character to see it through.