The Cost of a Non-decision
Making a decision has consequences. It's simple, you're faced with a fork on the road, you take a right, you made a decision. I praise you for doing so.
On the other side of the coin, there's significant cost associated with a non-decision. "Indecision" is defined as the inability to make a decision quickly. "Non-decision" is the inability to make a decision, period.
Whenever someone depends on your input, being assertive is paramount. You won't always make the right choice. Nobody is expecting you to, we're all flawed. But you must not stall progress by failing to choose.