A sort of unspoken rule it abides by to give its victims a fair chance.

Worse yet, the only reason you have potential of escape and it's 'held back' by the blinking is because, Depending on the Writer, SCP-173 treats the whole thing as little more than a game.

If you can't see it, it moves at inhuman speeds, almost silently. yet somehow it can excrete substances that seem like a combination of blood and waste. It's animate, but experimentation has revealed no actual signs of life. It's like the Weeping Angels put through a creepypasta filter.

It kind of doesn't help that its face, head and body in general kind of resembles a grinning baby reaching out for something.

When you hear scraping noises signaling that 173's nearby.

Or when you blink and he suddenly appears in the room with you.

You're just walking down the dark hall with the creepy ambiance playing when you turn a corner and find SCP-173 right in front of you, very close to killing you.

If you examine the scene closely, you'll see a broken air-duct where 173 escaped meaning that it could be anywhere in the building. 173 then kills two D-Classes and a guard while the lights flicker and when the lights finally die completely, it's gone with you as the only survivor.

You are escorted to SCP-173's cell and everything's fine at first, until the doors start malfunctioning and the lights flicker.

Scp 106 pocket dimension plane