Instilling Confidence

How do you instill Confidence in you children?

I shall set the scene and maybe you my readers can help me.
Tonight we went to visit our local Army Cadet centre. Son has been talking about wanting to join Royal engineers after finishing school, so it made sense to me to try and join the cadets as this will give him chance to experience a little of what he may expect later in life. While there daughter asked a lot of questions, i got all of the information we needed to join while son stood very quietly looking shy and nervous. The Staff there were lovely and made us feel very welcome. They agreed that it would be a good idea and that son would get over his shyness quickly and have a really good time.

Once home, Son was very quite and after sending daughter to bed i chatted with him and found out he wasn't sure what he wanted to do now. His view is that he couldn't do it, he couldn't remember it all, he'd never be good enough. I tried to re-assure him that he was and that he would learn everything needed.
Not long after i had  tucked both children in bed and was downstairs to do some chores. Daughter came down about 10 mins later to say son was crying. Son doesn't cry very often, not even when hurt so this was strange.

He was crying about the same things we had talked about downstairs. He he been 'kicked out' of Gifted and Talented as he put it. And therefor he can't do the GCSE he wants to do as you are invited to do it. That then means you can't do the courses at Uni he wants to and work where he wants. He's also worried that by changing his mind and not joining the Engineers he will let his dad down.

How do you console a child who's hormones are now beginning to work properly, and who's convinced he's not good enough. It broke my heart to hear him. My son is a warm, caring, talented and very intelligent child and now sudden;y he feels not good enough. One thing i do know is that it doesn't come from any bullying. I have always told him that i don't care what job he does as long as he's happy. And that if anyone tries to tell him he's not good enough then they can come and answer to me.
Yet this doesn't seem to be enough. So what do we as parents do to encourage our children and boost their confidence?

xx