You don't have to do everything. If you try to you will be overwhelmed and unless you're a genius it will become demotivating if you think you have to learn all

You don't have to do everything. If you try to you will be overwhelmed and unless you're a genius it will become demotivating if you think you have to learn all of it. Do you want to work on large or small jobs? For large jobs you will need to know a lot about reliability, scalability and sometimes performance. PHP or whatever language you work with is only a small part of the puzzle. For small jobs you will have to know the browser quite well (CSS, JavaScript/JQuery).