How many times throughout the duration of one day do we say "I don't like this" or "I don't like that"? How often do we use the word "hate" (even when we say we don't mean it)?
These were all potential opportunities for cultivating a happy mind, but instead of accepting conditions as they are, we fall victim to our preferences, wish that circumstances were other that they are, and subsequently begin to suffer.
An inverse relationship exists between hate and happiness; the more we hate, the harder to be happy. The more we're happy, the harder to hate.
Practicing meditation develops a multitude of different skills, one of which is the ability to objectively observe our experience with a calm and accepting mind. Making an effort to not judge the experience, we aim simply to observe the object of meditation as it is, not wishing it to be otherwise.
As we develop this skill "on the cushion", we bring it into our daily life. Carrying this same calm and accepting attitude throughout the day, we find more happiness and peace of mind amidst the inevitable ups and downs of life.