Being the first to step into the light makes you very vulnerable to attack.

I believe that when a "big enough" leader finally steps forward, they give people tacit permission to join in. The leader can't be just anyone, though. He or she must be someone that people recognize as a leader - someone with enough stature to provide sufficient protective shade from the harsh glare of public attention.

People who aren't yet recognized as having sufficient stature may come out first, but they are not likely to block enough of the sun to give those waiting in the wings the protection they feel they need in order to step forward.

They are leaders, but small leaders. The protective shadow they cast is not long enough.