Reliable and unreliable happiness

It has been wisely said that "happiness is an inside job". Everyone who meditates knows that to be true and non-meditators often intuitively know it as well. But here's the thing: we also experience happiness (or at least something that feels like happiness) from outside conditions too. That's what makes us crave what we want and prefer. So how to put these two experiences together? Meditation teacher Kathleen MacDonald says this:

We do experience happiness with things outside ourselves, but it doesn't truly satisfy us or free us from our problems. It is a poor-quality happiness, unreliable and short-lived. This does not mean that we should give up our friends or possessions in order to be happy. Rather, what we need to give up are our misconceptions about them and our unrealistic expectations of what they can do for us.

I really like the point that a happiness based on exterior conditions is unreliable. That truth is a big contributor to my motivation to keep meditating. I want an approach I can count on!