Где хотенье, там и уменье

When a person is determined to do some job, however difficult it may be, he will learn how to. See Была бы охота - заладится всякая работа (Б)

Cf: All things are easy, that are done willingly (Am.). It is easy to do what one's own self wills (Br.). Nothing is impossible to a willing heart (Am., Br.). То him that wills, ways are not wanting (Am.). Where there's a will, there's a way (Am., Br.). You can do anything you want to if you want to bad enough (Am.)