There is one wall in your home you look at more than any other. It is usually not the one you decorated. It is the one opposite the chair you sit in when things are difficult, and most people have never chosen what is on it.
Repetition is the whole mechanism
Anything you see daily stops registering as new information and starts working underneath awareness. This is why advertising is repetitive rather than clever, and it is the same mechanism whether the thing on your wall was chosen carefully or arrived as a gift in 2014.
The question is not whether your walls are influencing you. It is whether anyone chose what they say.
A sentence you see three hundred times stops being read and starts being believed.
Why one sentence beats a picture
A landscape is pleasant and says nothing in particular. A sentence has a direction. On a hard evening, an image gives you somewhere to rest your eyes; a sentence gives you something to hold, which is a different service and usually the one being looked for.
It has to be a sentence you would actually say, though. Anything that reads as instruction becomes irritating by week three, and anything that reads as slogan stops meaning anything at all.
Choosing the wall before the print
Work out where you look first. Not the feature wall, not the one guests see. The one in your eyeline from the sofa, from the desk, from the side of the bed at two in the morning. That is the wall doing the work.
Then choose for that moment rather than for the room. What you want opposite the chair you sit in when it is bad is different from what you want in the hallway, and it does not have to match the cushions.
On printing it yourself
A framed print is a small decision that people postpone for months because it involves shipping, sizing, and the possibility of getting it wrong. Printing at home removes all three: you can have it on the wall tonight, and if it turns out to be the wrong sentence for that room, you have lost a sheet of paper rather than a purchase.