If it's that easy to change yourself, there would be less mass shootings, lonely desperate men, and suicides in real life.
If it's that easy to change yourself, then Holly's character arc is moot because she should just change herself for the better without Ian and Lena.
Sometimes, a caring and sympathetic person is needed to bring you out of your endless slump and start making changes for the better. Depression, anxiety, and timidity are real, my dude. It's not something you can just 'suck it up and move on', you need outside help.