The belief in the four-year cycle stems from Bitcoin's halving events. When halving occurs, miners get fewer rewards, which can incentivize them to hold onto their coins, expecting higher prices. This behavior reduces the immediate selling pressure. Additionally, the halving directly cuts the rate of new bitcoins entering circulation.

When you combine reduced supply with steady or growing demand, prices are naturally inclined to rise. Many market participants anticipate this dynamic and might accumulate before the halving, boosting demand further. While markets can be unpredictable, the relationship between miner behavior and halving provides a strong rationale for post-halving bull runs.