A saddle is a leather seat for horseback riders. If you saddle something, you either put a saddle on it or you burden it with something else. If you buy an expensive saddle for example. you may be saddled (or burdened) with debt.
A saddle makes a horse's rider more comfortable and secure — and if you ever ride a camel, you'll also sit on a saddle. As a verb, to saddle means "to put a saddle on an animal," although it also has the figurative meaning of "to burden." Your excessive spending might saddle you with debt, or your position as the oldest of eight siblings could saddle you with too much responsibility.