This is why and how Alabama lost:
1) They have had a suspect defense all season long, and Clemson took full advantage. In the grand scheme of things, Alabama still has a good defense, but it was nowhere near the rock it has been in seasons past. Clemson had an uncanny ability to convert 3rd and long, and torched the secondary all night long. Alabama was extremely lucky Clemson did not put 50 on them as they easily could have done so.
2) Alabama's offense sputtered waaay too much, especially in the red zone. They were able to move the ball fairly well between the 20s, and Clemson actually gave up plenty of 5-7 yard chunks on the ground. The Tide controlled the clock for most of the game, and should have stuck with the run. Tua was not used to seeing a defense as aggressive as Clemson's and they made him look like well, a sophomore at times. They got too fancy, and as a result, found themselves unable to finish drives. They left quite a few points (probably 17ish) on the field.
3) Clemson simply wanted it more. They have been savoring this opportunity for a full year, and executed an incredibly masterful plan. They weren't necessarily flawless, but Clemson is the only team that doesn't have to be perfect to beat Alabama. They landed haymaker after haymaker, and left Alabama absolutely shellshocked. This is a team that is used to dishing out punishment, not receiving it.
This is clearly not the way Alabama's seniors wanted to go out, but for Saban, The Process continues. This will be a learning experience for the underclassmen and Saban will most definitely use this game as fuel for next season. I have little reason to doubt they'll be deep in the playoff hunt again in '19.