Not having wandering thoughts does not mean not thinking. 

 Having focused on our task, 

we do not dwell on it, 

lingering over failures or successes. 

Hearing that we should desist from wandering thoughts might sound like we should avoid all thinking. Not so. Wandering thoughts refers to incorrect thoughts, not all thoughts. When we have a task, we need to consider how best to accomplish it. And so we have correct thoughts. If others criticize how we do the task, we need to weigh the criticism. Is it valid? Or irrelevant? These are more correct thoughts. 

But what if we keep replaying the criticism as if it were a favorite movie? We’re right back at trivial, wandering thoughts. Why? Reminiscing about successes depletes our good fortune. Recalling failures plants the wrong kind of seeds. Embarrassment, guilt, anger. Either way, we end up not paying attention to our current tasks. 

So, do not linger on the past. Learn from it. Then move on so you can increasingly focus on correct thoughts.