Melanie’s sunny thoughts shine through in her mood. She’s optimistic most of the time, even when problems arise. Life just feels good to her.

But for Rhonda, even when life offers smooth sailing, she rationalizes the possibility of storm clouds forming just beyond the horizon. Worry gnaws at her as she remains on the lookout for potential problems.

Think about this: You can’t evoke thoughts by feeling a certain way. But you can evoke and, to some degree, control feelings by directing your thoughts.

So having control over our own thoughts gives us power to direct our feelings. But our feelings aren’t directed solely by will. We can’t just choose our feelings. Still, we can guide them with our thoughts.

That’s important because our thoughts are the origin of our behaviors. Each behavior begins this way: A thought stimulates an electrochemical response, which produces emotion; emotion results in an attitude; attitude produces behavior. This process affects the way we think and feel physically. So negative or toxic thoughts produce toxic emotions. Those produce toxic attitudes, which result in toxic behavior.

Our ability to think and represent things to ourselves also enables us to bring vast ranges of reality—and nonreality—into our lives. Basically, that means that with our thoughts, we can usher good or bad things into our lives, real or imagined, depending on the content of our thoughts.

Welcome to Thought Chemistry 101

Are your thoughts harmless or harmful? Well, it depends.

It’s important to understand that our thoughts aren’t isolated or disconnected. Each time you have a thought, it triggers an electrochemical reaction in your body, whether you’re aware of it or not.

That’s right, each thought sets of a biological process—about 400 billion at once. Because of that thought, chemicals surge through the body, producing electromagnetic waves. Those set of emotions, which affect how we behave.

We listen to our emotions and act upon them. For instance, when we’re fearful or worried, we may act by withdrawing, or attacking, or blowing a situation out of proportion. Whenever you have a thought, and that electrical transmission goes across your brain in a fraction of a second, you become aware of what you’re thinking.

Ever wonder, when you’re feeling good, why you’re feeling so good? Why you’re feeling positive or happy? There’s a simple reason for this. It’s due to those chemical reactions set off in your brain as a result of your thoughts. Bad feelings and attitudes arise from this process too.

That’s because some of the chemicals that are triggered by our thoughts are “feel-good” chemicals; others are “downers.”

How Your Thoughts Shape Your Character

You may wonder, aside from affecting our moods, does it really matter what we think? We’re just talking about harmless thoughts, right?

Wrong. The truth is, the content of your thoughts matters a lot. You see, our thoughts can limit who we are and what we become, or they can act as the catalyst prompting us forward in our lives.

Our thoughts influence our character, shape our attitudes, determine our behaviors, affect our spirituality, and even influence the immune system, says author, educator, and psychologist Archibald Hart. “Your thinking determines whether you will be happy or sad most of the time. It even determines if you’ll get married and whether your sex life will be satisfying,” he says.

Let’s assume this day isn’t going so well for you. There have been frustrations and setbacks—other people not following through on commitments, loved ones not paying attention to your concerns, children misbehaving. You’re feeling like Rhonda usually does, like nothing ever goes her way.