Just over two millennia ago, Mithridates became king of Pontus. As a child, his father had been killed by poisoning, and Mithradates was determined the same fate would not befall him. And so, throughout his life, he deliberately strengthened his immunity to the various known poisons of his day. He did this by both seeking out and combining natural antidotes, as well as by ingesting non-lethal doses of various poisons on a regular basis.

That’s right, to keep his body fortified against poison, he is said to have intentionally ingested these poisons in small doses. The goal was for his body to develop an immunity to the poisons that would-be assassins may try to kill him with. And it worked. So well, in fact, that when he was surrounded by the Roman army at the end of his life, he tried to poison himself—and failed. He had fortified his body so well against them that they didn’t work the one time he hoped they would. And so, to escape being captured, he had his bodyguard kill him with his sword.

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Now, ingesting a little poison every day is not something most people would willingly do. But for Mithridates, there was a reason for this practice. Over time, his body grew in its ability to handle these toxins. Just like exercising a muscle, the stress caused the body to adapt and get stronger.

The same principle holds true in other areas of life. If you stretch yourself a little every day—if you’re regularly facing a fear or taking a step—you’ll see yourself grow over time. This doesn’t mean that some things will magically become ‘easy’ or stop being ‘scary’. But in time, you’ll be better able to deal with them than you when you started. For Mithridates, the poison didn’t become less poisonous because of his practice—it’s just that his body grew in its ability to deal with it effectively.

Intentionally exposing yourself to a little bit of difficulty here and there can be beneficial. These difficulties can trigger a response that makes you stronger in the long run—whether in mind or body. But this same principle can also play itself out in a different direction.

It’s one thing to intentionally expose yourself to toxins in order to develop a strong immunity to them. It’s another to unintentionally allow them to slowly wear you down. Consider someone who has been exposed to carcinogens throughout their life. They weren’t exposed to lethal amounts—just a little here and there—but eventually they develop cancer or some other potentially fatal condition as a result. Day after day these toxins were having an impact, but instead of producing strength in the long run, they were actually creating weakness.

The same can happen in life. Little by little, we can expose ourselves to things that can negatively affect our bodies, our minds, our hearts, our relationships. Instead of strengthing us, they end up weakening us. But because the dose is so small, we may not even notice until they’ve already begun to have an effect.

This is why paying attention to your daily habits is so important. The little things you expose yourself to day after day will have an impact in the long run—whether for good or for ill. And although I don’t recommend going as far as Mithridates did with his intentional ingestion of poisons, you can still follow the same principle of intentionally exposing yourself to the right kinds of difficulties for the sake of long-term growth.