For some reason unknown, Ukrainians believe so which resulted in that atrocious situation where both the US and European countries are not willing to step in and protect Ukraine. Even Zelensky himself had high hopes for that, based on what he said a few days ago.
Both US & EU are lending tremendous support in materials, training (over the past 8 years), and coordinated economic sanctions far beyond what anyone would have predicted. Sounds like Europe is also offering energy grid support soon.
What those countries will not do is directly intervene using their own military forces – Ukrainians would have to be crazy to ever expect that. Two nuclear-armed powers in direct conflict on the battlefield = nuclear holocaust. You could say that's merely conventional wisdom based on wargames and other geopolitical assumptions, but... does anyone really want to test that theory??
But the sanctions are meant to make people angry, go out and send a strong signal to their leaders they want a change. This is the most the West can do.