What causes women to become indicisive?

It's not really limited to women.

People become indecisive all the time regardless of gender.

Typically this may be chalked up to changes in hormones, changes in blood pressure (leading to confusion), lack of experience under pressure or any of a million other variables; none of which are technically gender specific.

From a less clinical view, it may be said that traditional gender roles may put women into situations that trigger these variables more often; but it's just as possible for men to become indecisive.

So the real questions are, what makes any human become indecisive and why are women forced to face those situations to such a degree that you personally see those triggers more often compared to men? I think those answers will be different for every person you ask, including yourself.