The Cod Army sacked manager Micky Mellon despite two promotions in the past three seasons and a League Two play-off spot at the time of his departure - a position that was surrendered with a goalless draw against Southend in Alexander's first game in charge.
The former Scotland international, 41, played more than 1,000 games across three decades and refuses to be intimidated by the prospect of suffering the same fate as his predecessor.
He said: "If you weren't slightly worried and concerned about different things then I think you go in with your eyes half open and you're going to make mistakes along the way.
"I'm cautious in the way that I go about things. I think everything through.
"I know I'm coming into a club that's been successful in its recent history. I'm here to continue that.
"Am I afraid of being successful? No. Am I afraid of being a failure? Yes, I always have been since I was 16 years old when I first came into professional football.
"That's the fear that's driven me on, that I had to succeed to be in this game for as long as I could and that's how I'm going to attack this."