The above quotation is from the incomparable, Leonardo Da Vinci, of which there are many, many people that would behoove themselves to take this advice to heart, for it is straight to the point and so very true.
The thing is that people do all sorts of things every day, of which a portion of these things, and for some of those people, a very large portion of it, are doing things and getting involved in activities that they really shouldn't be doing, for these activities are not beneficial in the long run, nor are they even necessarily beneficial in the short run, but somehow or other, they can't resist continuing to snack, or watching mindless television, or endlessly look at one social media post after another.
The very first thing to remember is that you are sovereign over yourself, and further that your decisions do matter. Additionally, whether consciously cognizant of this or not, people are often creatures of habit, primarily because they have time commitments to their job, to their school, to their family, to their meals, and so on and so forth, in which in order to accomplish these tasks, habits are typically formed. It is in the structure of these habits, that people need to take more time to consider them, for habits, good or bad, once they become part of our routine or structure, are exceedingly hard to break free of.
The reason that habits are so difficult to break, is that they soon become thoroughly ingrained within us, which often allows us to free our mind and to thereby think or to dwell upon other things, yet, we still should periodically review our habits, and should consider as to whether they should or should not be our habits in the first place, and if not, to change them.
It is always easier to resist at the beginning because not only has the habit not been formed, but because at the beginning, we recognize that we have a multitude of various options, that we can avail ourselves of, in addition to the fact that we have yet to become biased in regards to confirming that having thought and made a particular decision, that such a decision must be the right one, even when the evidence being presented to us, appears to negate that view.
People, often do not want to admit to a mistake, especially when they have invested time, money, and their reputation to it, in which, that makes it even more difficult to extricate themselves from that decision, for they believe that it often makes them look foolish to make that change, even though using their willpower and determination to undo what has been done would be better, but because they are in so deep, their reluctance to do exactly that, has been weakened, considerably.
You will not need to worry or bother yourself about resisting certain undesirable deeds, if you do not begin such in the first place, for these things not being part and parcel of you, means that they do not have a hold upon you, whereas if you give in, once, and then again, and then again, the hole that you are digging, will just keep getting bigger, till you find that you are in so deep that you can't readily escape so you may as well just live with it, all because you weren't able to resist at the beginning.