Your description of your experience with cannabis is telling. If you're frustrated with not being able to hold a thought for more than 5 seconds, then that might mean that you went into it with expectations of how it should go, and then spent your time being high trying to retain the "control" you had sober and bring those expectations to reality. This is a common mistake. The good parts of cannabis come from letting go of expectations of control. It's in letting go that hyper focused states or creative bursts can happen.

Not everyone is able to "let go" at will, but some can do it intuitively while others may have anxieties regarding control that must be worked through.