The Real Madrid goalkeeper was part of the World Cup-winning side in South Africa four years ago, as well as the team that triumphed at the UEFA European Championships in 2008 and 2012.
Casillas will also likely be Vicente del Bosque's number one in Brazil as Spain seek to continue their recent dominance in international football.
However, the 33-year-old knows Spain - in a group that includes Australia, Chile and the Netherlands - are just one of a number of teams with a realistic chance of winning the tournament.
"We have a difficult group. In addition, our first two matches are against (the Netherlands and Chile) who, in theory, we will be vying for qualification with," he said.
"I think we need to go to Brazil without any pressure.
"In these last six years we haven't done good things, we have done sensational things. We have earned the right to fail."
"We are going with the idea of competing and defending our title, but we know that there are 31 other teams who want to do the same and it won't be easy."
Spain are again among the favourites in Brazil.
Casillas believes Group B rivals the Netherlands could be a threat in the latter stages, stating Spain's tough opener against Louis van Gaal's men will stand them in good stead.
"From what I hear from people, I think the Spanish fans are delighted with the last six years they have seen. The majority thought they would never see anything like it," he added.
"We start against Holland, who should be the other big favourites along with us.
"However, I think that having to start strong gives us motivation. It means that the team must be in the right mindset from the first day."
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