What is the ruling on lying to oneself by saying, "I am strong" or "I am intelligent" in order to achieve that?

Speaking to oneself in a way that contradicts reality is not considered a lie, because it is not a truthful report. Rather, it is akin to optimism and self-encouragement. A Muslim should seek Allah's help in all their affairs, for success comes from Him, glorified be He, and failure occurs when one entrusts oneself to oneself. The key to goodness is supplication and a sense of neediness before Allah.