Constant qualification is the process of continuously evaluating all of your opportunities to check that you still want to and should be bidding. It is possible to get caught up in an opportunity that you are unlikely to win and that diverts valuable resources and time from other more suitable opportunities.
Firstly, you need to understand the importance of having a formal bid/no bid process. This is to help you understand when and why you should bid, and to make sure you avoid projects that you have a low probability of winning. Sometimes a decision is made early to bid but is that still the right decision as you learn more about the opportunity?