There is little more poisonous to a team than an indecisive leader. Note that this is very different from rashness. If you have time to make a decision, use it wisely, but remember that you will never have all the information or assurances you want, and you will have to act on incomplete or even contradictory information.
The key is to fail quickly and cheaply (how many projects continue to consume resources long after it is clear they will not deliver the benefits originally anticipated?) and to maximise the value of the right ones. Good communications are essential here.