The best parenting advice I ever had was unsolicited and from a complete stranger; an older woman with whom i'd struck up a conversation in a cafe. My daughter was a few months old and I'd commented on how I could already see she had a completely different temperament/character to my eldest. Not in a critical way just in an, "I'm amazed it's so obvious," way.
She said, "Parent the child you have. Not the one you wanted or the one you think you should have. Not the one in the books but the one right in front of you."
Someone had said similar to her and she said it had really helped.
The meaning being that theories/schools of thought are great but they are just that - theories. Your child isn't interested in theories. Some children are naturally more confident, outgoing and some children are naturally more reflective and like to sit back to get the measure of a situation before getting involved. Just like adults...
Resilience comes from having confidence in their abilities, confidence that you will he there for them, making mistakes and learning from those etc.
I did similar to a pp - from a young age they were encouraged to ask for the children's menu or where the toilets were. They received support and encouragement. I didn't jump in to solve all their problems for them but gave them strategies for dealing with it themselves. Let them know it's OK to make mistakes and don't be embarrassed by them if they are not doing something in the way you think they should. Don't compare to other children.
When I could tell they needed more from me, I gave it.
I let them see that they could do things by themselves but they knew I was always their safety net.
They had a safe space to voice their thoughts and feelings. And I was one of those 'only on MN' parents who didn't shout. They were told off if they were naughty but it was respectful. I didn't mock or shame them. I listened to them. They felt they had some control. Not that they were in control ever but that they always mattered.
They're now 26 and 18. Both are confident but it took time through repeated experiences of 'mattering'.
Your son is 3. He's very, very little. There will he sometimes when he feels confident and others when the world and the people in it are huge and scary. Watch for what he is telling you about how he feels in a specific situation and respond to that..