OldStyleMuayThai has an article on the importance of power, especially in practice.

In a streetfight you have about a three to eight second window of opportunity to finish your opponent and get away before it becomes more dangerous for you.

After the window of opportunity is closed anything can happen and it’s usually not very good.

You can both end up on the ground, more than one adversary can appear, weapons can be drawn against you, and your energy will be severely drained.

So why would you be throwing love taps at your attacker when he is totally committed to ripping your head from your shoulders and kicking it down the street.

There is no reason why anybody should be sparring with their adversary when in a streetfight.

That’s why I tell people to have intent when they train in the gym or dojo, spar like you’re in a streetfight, and not like you’re in a cardio boxing class.

While he’s talking within the context of fisticuffs, really the principle is applicable to any context. And it’s summed up in one line:

GET REAL AND START TRAINING LIKE YOU MEAN IT!!!

Whatever the reason you’re training, remember that reason. When you are training, train towards that goal. So if your goal is self-defense, hit that punching bag like it’s someone intent on ripping your head off. Shoot that target like it’s someone intent on raping your wife and leaving you for dead. Put your mindset where it needs to be.

Granted, not all training sessions can be this way, and it’s not always applicable. For instance, I may be training for a competition instead of self-defense; that is, I may have multiple goals that I’m working towards. That’s fine, because the key remains to not just go out there and tap the bag or fling lead downrange or whatever. Set your goal, work towards it.