how to instil a huge

how to instil a huge sense of self-doubt in someone: lesson one:
make that person ponder whether or not they are, in fact, dull, living in the dullest place on the planet, leading a dull life, even if, previously, they believed they were not dull (well, not entirely), the place they lived in wasn’t dull (not very exciting, granted) and their life wasn’t in the least bit dull (hey! I bought a loo seat today! and ate a goose’s egg!).
my confidence has just been zapped.