The first half of their post-14nm stagnation was because they were overly ambitious for 10nm. But the second half of that era was because of their hubris, denial that things weren't going to plan, and inability to adjust plans. They eventually admitted defeat (to some extent) and back-ported one of their 10nm designs to 14nm as a stopgap, but they started that effort at least two years later than they should have.