why it is so hard to learn a new language by myself?

I am Chinese,and I want to learn Spanish.

I bought one book in 2014,so I started to learn it by myself. But the speed is very very slow. At present ,I only learnt 5lessons. It is so easy to forget and hard to remember.

I  analyzed the main reasons:

1. Too free,no pressure;

2.without environment;

 Is there anyone who has the same issue with me ? Do you aggree with me ?