Why didn't Vegeta know Cell was about to destroy him?

[kriss-]

I swear, it's another plot-hole. Vegeta should have known he was fucked right from the beginning. Trunks SSjG2 tries to punch Cell as he's transforming, but he can't even get past his aura.

Chapter: 379 (DBZ 185), P11.4
Context: Vegeta talks to second form Cell
Vegeta: “Heh. I’ll tell you something that will really shock you! There’s a guy named Trunks over there. He’s not as powerful as me, but we’re pretty close…!”

Spoiler

Why didn't Vegeta know right from the start that Cell was about to kick his ass if Trunks was useless against him?

 

[withheldforprivacy]

I don't think punching a barrier is the same. But, yes, you can say Vegeta was really blinded whenever he achieved a new form. Remember when
he wanted to take 16/17/18 all three at once, even though he knew they were at least a lot stronger than Nineteen, which he debatably couldn't
one shot.

 

[Clearin]

I did a quick check to see if Trunks had definitely turned grade 2 by that point, and indeed he had, but I noticed something kinda weird...Trunks doesn't actually turn grade 2 until after Cell spots #18 and charges after her, just before that he was standing right in front of Cell clearly ready to take him on. Does that mean regular SSj Trunks is stronger than Semi-Perfect Cell?

And this is something that probably only matters to me, but the fact Trunks uses grade 2 specifically to catch up to Cell and stop him would prove that grade 2 does increase speed (or at least doesn't lower it). I'm sure most people already knew that, but I personally thought Goku's explanation of regular SSj being the best balance, saying "all this muscle decreases speed" and grade 3 being "one notch above" grade 2 meant that both forms sacrificed speed for power.

As for your question, it could be that the "aura" around Cell was actually his barrier which was used to make sure no one interrupted the transformation process.

 

[Let's Go Fearless!]

Vegeta's ego is huge back then.

 

[Zippy]

As for your question, it could be that the "aura" around Cell was actually his barrier which was used to make sure no one interrupted the transformation process.

I agree with this notion

 

[Jeff Styles]

Vegeta is blinded by his ego to admit or think when someone may be stronger than him after he have gain a new form/power up.

Cell's aura seems to be his new power formed into a shield, so his transformation is not stop. The first time a hero decided to try to stop a villain from transforming, it shown to be in vain.