When I got first got my puppy, I fully intended on socializing him as much as possible, because I thought that was the right thing to do. In puppy school, he was the quiet one. He didn't leave my side and wouldn't play with the other dogs during the designated socialisation time. The trainer told us to pick him up and put him in the middle and he'd just walk right back to me. He did watch them very curiously though and would wag his tail when he saw them playing with each other. It seemed he was just unsure of himself.
At the beach he would walk flush up against my leg, never leaving my side (no leash) and even tucking in his tail when little dogs barked at him. These behaviours made me think I had a timid puppy who would eventually grow up to become fearful dog. Despite everything online saying socialise socialise socialise, I decided to give him a break and build his confidence at home while limiting the chance of anything traumatising happening to him in the outside world. Now at 16 months he's bursting with confidence! He loves every dog and person he meets and if the dog is snappy he just moves along like nothing happened. I saw the shift from around 6 months on, and couldn't be happier with him. He was clearly out of his comfort zone when he was in these situations as a puppy, and I'm glad I didn't push him too much.
We did start go to a training club when he was around 5 months old, which I figured should be fine since it's a controlled situation. There are a few different trainers there who have met him on separate occasions and all of them have commented on his great disposition.
We played a lot of tug (letting him win almost always), lots of positive reinforcement, and limited exposure to potentially nasty situations. Not as much socialisation as I intended, but I'm so happy with the outcome