Your example is not a compound sentence of two independent clauses.
The "also" makes the second part a dependent clause
Robert explains that being a good banker isn't enough to become rich, one also has to be a good gambler in order to understand the price to pay.
Robert explains that being a good banker isn't enough to become rich, (and) one also has to be a good gambler in order to understand the price to pay.
Your two independent clauses are
1) Robert explains that being a good banker isn't enough to become rich.
2) One has to be a good gambler in order to understand the price to pay.
both can be understood independently.
By adding "also" to the second part
One also has to be a good gambler in order to understand the price to pay
it can no longer stand alone and make sense since the reader is left wondering "also what?" which now makes it dependent on the first part.
"And" is not necessary to combine the two as pointed out in the comments, but the meaning and understanding does not change with or without an "and".