I first joined a gym when I was 17 and that was mostly because it was cheap and had a hot tub.
Since then I have taken the gym slightly more seriously but never bothered to learn properly how to use one. I always saw the price of a personal trainer and thought 'meh, I've been picking up heavy things all my life, I think I have a handle on technique'.
Coming to terms with the need and how expensive a personal trainer might be is key I think, to anyone looking to gain muscle. Think of it as an investment - once you know how to do things right you can do most exercises on your own.
It's like being taught to bake bread. Anyone can throw flour and water in an oven, but you're not going to impress any girls with the outcome unless you get taught some technique.
By seeking out help you are not only shown new exercises, but you also inevitably find out how many you have been doing can be improved.