At any turn a player is expected to have one or more "reserve words" in mind which could be formed from the exact word-stem in play.
However, a player can opt to bluff on their turn - that is, they can add a letter to the word-stem without actually having a reserve word in mind.
Bluffing is almost always done as a last resort, though some players may use bluffs strategically to force their opponents into untenable positions.
But simply extending the length of a word won't guarantee a win.
In Example 1, it can be noted that the phrase "AT" does not end the game; this is because words only become valid once they are at least three letters long.