A capitalist who invests indiscriminately (e.g. broadly) today, has a positive expected outcome of this, and that's not a given out of the fundamental theory.
The work a capitalist does, their contribution, isn't just writing checks, it's writing the right checks.
It just happens that a capitalist writing a large number of checks happen to write a couple of right ones. And often we need them to write some wrong ones too.
The work a capitalist does, their contribution, isn't just writing checks, it's writing the right checks.