To manage packages conveniently, I set new load-path by (add-to-list 'load-path "c:/emacs/.emacs.d/lisp")

After that I checked load-path lists through C-h v load-path, which confirms "c:/emacs/.emacs.d/lisp" had been added into load-path lists successfully. Then I run (use-pakage xxx) inside my custom init.el, but a warning occurred said

Error (use-package): Cannot load xxx

I rechecked load-path lists and move packages to another one directory mentioned in load-path lists, which is loacted in Emacs installtion directory named site-lisp. THEN (use-pakage xxx) returned to normal and didn’t rose a warning.

It’s so weird, and I just want to set a custom packages load-path. Does anyone know what goes wrong?