Unintended consequences can be roughly grouped into three types:

1. A positive, unexpected benefit, usually referred to as serendipity or a windfall).
2. A negative, unexpected detriment occurring in addition to the desired effect of the policy.
3. A perverse effect contrary to what was originally intended, when an intended solution makes a problem worse

For Walt, the unintended consequences are cutting all three ways.

It's true. In episode 512 if Walt had not tried to meet Jesse in a public square...

And if that public square didn't happen to have that tough looking bald guy there at that moment...

Walt would have met with Jesse and either diffused the situation or gotten caught by Hank.

Instead, Jesse refuses to walk up to Walt, calls him to threaten him, which leads Walt to call Todd.

I'm pretty convinced Todd's uncle wouldn't have come for Walt if not for the blue color of the meth.

And the blue color? That dates all the way back to a seemingly inconsequential decision in season 1.