The world championship leader was forced to stop at the Variante Rettifilio five minutes before the end of the first session with an engine problem.
He then missed a chunk of practice two with first braking issues and then a gearbox that expired beyond its life date.
"It was just a little bit of a strange Friday because of mechanical failures," said Alonso, who was delighted with the balance of his car nonetheless having ended the day third fastest overall.
"Sometimes we push some parts to the limit to work some experimental things on Friday that you need to get some mileage on it and some experience.
"We need to take care and this was a good reminder again how important is the driveability of the car and how important it is to take care about any detail of the car because small problems stop the car immediately.
"Sometimes when something happens on Friday it will never happen anymore on Saturday and Sunday. So we will make sure that what happened today won't happen anymore.
Alonso, who stated earlier in the week that he would not race for any other team in the future, added that striking a good balance with the car so early in the weekend was a huge boost for his chances at Monza.
"I think we are more-or-less happy with the performance and we don't need to change the balance of the car for tomorrow, like we did [before] because we were not happy at all [with it]," he said.
"It's good. More than the performance it's just the balance of the car. Sometimes on Friday we find that we need to change the car completely for FP2 and then completely again for FP3 and then you can be in the middle of making decisions at the last moment before quali.
"So far in FP1 and FP2 we have found a car that was consistent to drive and we have seen both Ferraris in the top seven all the time, which it is not always like that.
"So that is the best news in terms of performance."