Ever tried to solve a problem by trying all possible solutions until you achieve the wanted result ?
In essence you are brute-forcing the solution, same applies to an brute-force attack in the encrypted world.

A brute-force attack is a crypt-analytic attack that can be used to decrypt data. When used for password guessing this method is exponentially more difficult with increased password size.

Obfuscating data to be encoded makes it harder to guess thus reducing the effectiveness of the attack. From another angle the strength of an encryption system equals how long it takes for an attacker to perform a successful brute-force attack.

In resume always use a long password (>16 characters) if possible and don’t use meaningful words. A password manager is recommended.