“Never discount your products.” is good advice.
If your customer is the kind of person who likes to pay full price, you’re doing both of you a disservice if you offer regular discounts and sales on your products and services.
On the other hand some people love that feeling of getting a deal and that drives a lot of their purchasing decisions. Without discounts they may never buy from you, ever. It pays (pun unintended) to know what type of customer you have so that you can serve them best.
It is worth noting that once you choose to discount and run sales, you’ll need to commit to doing them forever as people will come to expect them.