I loath feeling defensive when demonstrating an early version of anything I'm working on. This is especially the case for games - they just look like shit for so long. And everyone notices. All too often I have to guide the player's eye back to the point of what I'm demonstrating or requesting feedback on.

temporary assets are distracting

"So are those always going to be cubes?"

The answer is still no.

"Which one am I?"

You're the white cube with the selection indicator.

"Which way am I facing?"

Just try the controls, please... I'll be over there crying.

The next thing you know your mood is ruined. The flow of the whole demonstration is lost and you let the doubt and dread put one foot through the door.

early feedback is crucial to motivation

Momentum is huge when you are working on a small project with a small team, or worse yet, alone. Spending energy keeping your attitude above water is exhausting and can quickly slip into a degenerate situation.

so I spent some time making it prettier

No this still isn't it's final form but at least it looks like a game. I have definitely felt an improvement in demonstrations and hallway tests. People look at it and seem eager to figure it out now.

it's a lesson, but I'm not sure how valuable

There are plenty of games that still look like prototypes (Thomas Was Alone, Dwarf Fortress, Minecraft) so it's best not to take this too far. But if you are struggling with this issue like I have in the past it may be wise to spend some time making it look a tad more presentable earlier on.