Let's draw a distinction between being decisive and being impulsive.
Decisive: As soon as enough relevant information is gathered and analyzed, a decision is made promptly and consistent action immediately follows the decision.
Impulsive: As above, but generated by primarily by emotion.
Impulsiveness is always decisive, but it's decisiveness based on... well, on impulse. On emotion and the first grasp of the situation. Decisiveness can be done without being impulsive, by first gathering and analyzing the information.
Decisiveness is an incredible virtue. It's something extraordinarily worth cultivating and will produce tremendous benefits for you if you cultivate it.
Impulsiveness is a bastardized version of decisiveness. It's decisiveness, so it has tremendous value. But it implies acting on emotion without necessarily getting the full set of relevant facts.
The funny thing about impulsiveness is that it tends to perform really well until it starts performing poorly.
Then it performs really poorly.
For the vast majority of action, fast decisionmaking (decisiveness and celerity) is more important than getting the nuances right. Just getting started and getting into action is incredibly valuable.
The problem comes when you "go with your gut" and you're wrong. Being impulsive can gain you a lot of ground, but you can lose 50% to 80% of that ground in one bad decision.
An example: I just finished "Call Me Ted," Ted Turner's autobiography. He was a decisive guy and it made him a lot of victories. Sometimes he was also impulsive, and he had two or three transactions that cost him an immense amount of ground.
He moved quickly and overpaid for MGM, and then sold most of it back at a significant loss that was the beginning of many other problems.
Because of that transaction, he had to bring new investors into his company. He gave veto powers to two new investors which were later used against him.
And the extraordinarily disastrously bad AOL-TimeWarner merger.
By being decisive and crossing slightly over into impulsiveness, Ted built his fortune. But those three transactions cost him somewhere between half and 80% of what he could have had, and eventually he got forced out of his own company. Heck, he might have had 1,500% more resources at the end of his career without those three.
Now, who cares, eh? What's the difference between $2 billion and $30 billion? Nothing?
Well, Ted cares a lot about the environment, on ending nuclear proliferation, and on promoting good relations and world peace. $30 billion would mean a hell of a lot more money into conservation, pollution cleanup, protecting endangered species, decommissioning weapons, and supporting positive global organizations.
At that magnitude, it doesn't make a difference for his personal lifestyle at all, but it does make a considerable difference for the causes he holds most dearly.
But again, he couldn't have become a billionaire in the first place without being extremely decisive. The decisiveness is extraordinarily valuable, but the ideal decisiveness is a gradual, mature stripping out of excess emotion in the decisionmaking.
Achieving extraordinary decisiveness without any impulsiveness would be hard to do, but worth striving for. The combination means all the efficacy and speed of a decisive person, without the blunders of an impulsive one.