Norris finished where he started in seventh but struggled on the medium Pirellis during his opening stint to lose three places before pitting on lap five of 44 for hard tyres.
The Briton reckoned this part of the race was "terrible" as it left him trapped between defending through the first sector before then being unable to pass later in the lap.
He explained: "It was terrible - it's an honest answer. We were just stuck in a circle of not being able to push enough in the middle sector because of the cars ahead and people [behind] having to lift in Eau Rouge. We were that slow.
"I was getting overtaken before the DRS zone even started. So, we had to try something. We went on to the hards and this was even worse. No one's ever used the hard all weekend.
"We thought it normally kind of suits us, so I think it was the right decision to try. But it was still terrible. I didn't have enough laps to get the tyres in and be able to push.
"I got overtaken on my first lap out of the box."
Norris added that his tyre struggles came independently of the MCL60's downforce levels, saying it is a deeper-routed issue that the team has battled for five years.
He continued: "[It's] how we treat the tyres with suspension. Everything like that is not where we want it to be. It's about the balance, not just about adding load to the car."
Given his turbulent race start, Norris reckoned he had no idea how he managed to recover to seventh at the flag. He said it felt as though he was last for most of the race.
"Then we put the soft on and everything came back towards us," he explained. "I don't know how I ended up P7. Honestly, I felt like I was last for the most part.
"So, a little bit surprised, honestly. We just need to rethink how we approach the weekend.
"The wing level and stuff like this might work on [this circuit], but it doesn't work on all of them. And we clearly got it wrong."
Norris thought McLaren struggled to refine its car set-up at Spa since the team had been focused during recent races on optimising its major car upgrade package.
He said: "All of the focus was on doing that, which is the correct thing to do."
However, team principal Andrea Stella brushed aside any correlation between the upgrades and race execution, instead saying that the design office has prioritised improving the overall performance at the expense of developing a low-drag rear wing for Belgium.
