There are times in life when just do it is NOT the answer. For an extreme example, someone is standing on a ledge obviously thinking of jumping a great distance resulting (more than likely) in their death. In that situation, telling them to just do it would be very inappropriate.
There are times in life where someone else (or maybe even us) is not on an actual ledge but definitely heading in the wrong direction. We feel we should warn them, but many people when you tell them what to do...they want to do the opposite. Telling someone (or ourselves) don't do it, even if it is for safety reasons can backfire. That should not keep us from speaking up though when necessary. This is probably how interventions start!
Then there are the times we need to tell ourselves don't do it. Maybe it is something kind of easy like just not having a second handful of peanut m&ms (yummm, oh wait, I digress). The more we want it, the harder it is to not do it. It's called temptation.
Tempt: to entice to do wrong by promise of pleasure or gain Temptation: the act of being tempted
1 Corinthians 10:13 No temptation has overtaken you except what is common to mankind. And God is faithful; he will not let you be tempted beyond what you can bear. But when you are tempted, he will also provide a way out so that you can endure it.
It is difficult to watch someone, especially those close to us, do things that we know are not good for them. That is when we need to maybe tell them once (or 2x), then back off, pray and let God handle the rest. We need to realize most of the time don't do it is not to cramp anyone's style. It is to keep them from harming themselves or others.
The Bible is full of don'ts. We can take that one of 2 ways. God is being restrictive and doesn't want us to have ANY fun OR God is providing boundaries that will keep us safe and keep us from self-destructing. Honestly, when left to our own devices? Most of us would do it and forget the consequences.
Genesis 3:22-23 And the LORD God said, “The man has now become like one of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever.” So the LORD God banished him from the Garden of Eden to work the ground from which he had been taken.
Do it! Don't do it! Choose wisely.