Should you buy more stocks from a company you already own own several months later ?

Pure noob here, there's something I'm having a hard time understanding.

Assuming I buy a stock $100 and I'm planning to invest in that same company regularly on the long run because can't buy 20 stocks at once.

Let's say this stock is worth $110 about 4 months later and I have fresh cash to invest. Is it a good idea buying this same stock at $110 again ? Wouldn't that be totally counterproductive towards the gains I already made ?

But then how are you supposed to progressively invest in a company on the long run without shooting a bullet in your own foot ?

Thanks!