The biggest mistake Danny made was waiting too long to choose a path.
We more or less had two teams the last two seasons.
The 'veterans': Irving, Hayward, Morris, Horford, Baynes (+Wanamaker/Larkin and Theis)
The 'youngsters': Smart, Rozier, Brown, Tatum, Williams (+ Ojeleye and Yabusele)
Both talented and both just not good enough to make the leap to contention. Ainge should have chosen a direction, either Irving-Hayward-Horford + to be acquired superstar, would need to be the championship core or Brown-Tatum + to be acquired superstar.
Gambling on a continuing championship roster (first lead by Irving, Hayward and Horford, then by Brown and Tatum) was too arrogant.