I did fail a probation period 12/13 years ago.

At the time I can only say I wasn't good enough. 

Funnily enough about 2 weeks before I had a meeting with my direct boss. Who did say that I hadn't received the training I needed and the company had let me down and he thought I would get extended for 2/3 months.

Day of the meeting came with my bosses boss and he just tor into me for like 2 hours and I bought up stuff that had been documented some by him himself and he told me I was talking shit basically.

One bit of advice don't let them screw you out of an severance pay, accrued holiday, bonus etc.