At the 2014 World Cup, the experienced goalkeeper committed costly mistakes in the 5-1 defeat to Netherlands and the 2-0 loss to Chile as the defending champions failed to progress beyond the group stage.
Casillas was again in the spotlight on Saturday when he failed to deal with a deflected shot and gifted Bakary Sare the only goal in Porto's defeat at Vitoria Guimaraes.
However, the Spain coach remains confident it will have no lasting effect on the 33-year-old and he will be ready to aid the national team's European Championship and compete for a starting berth with David de Gea.
"Casillas made a mistake, but the important thing is that he is well and arrives at Euro 2016 in good form," Del Bosque told Cadena COPE.
"I think he's already cured of fear. All goalkeepers make mistakes, it's impossible not to.
"[He] doesn't normally face a lot of shots [and it] requires more concentration."
Del Bosque hinted Athletic Bilbao's Aritz Aduriz and Paco Alcacer of Valencia could make his squad for the tournament in France having impressed with their displays in a Liga season which he feels is more competitive than usual.
"Many Spaniards are scoring goals. Aduriz is fantastic and Alcacer has not lost his eye for goal," Del Bosque added.
"We will look to forwards who have had a good season and complement what we want.
"I would not say there are three teams that are very good because a few others are having excellent season, making it a very tight league, which is what you want."