Excellent comments, @aztezcan. Glad to see you contributing here. Those are very useful for anyone planning a study where they may not be familiar with challenges in recruitment and accrual.
One interesting problem is heterogeneity in practice patterns within sites. One of our largest clinical services was an enrolling site in a major cardiovascular outcomes trial that is still ongoing (recruitment closed, follow-up still going). We enrolled only 1 or 2 patients because the physicians within that area had differing views on the trial and I think most really didn’t care to enroll patients, so eventually our site PI pulled the plug and admitted that our recruitment was likely a total bust.