Real took charge of their Champions League round 16 playoff with a 3-2 first-leg win in Manchester.
Guardiola said afterwards: "Today was tight and in certain times we had chances.
"Many games at the end we give away. In that level it is so difficult. It is not the first time, it happens many times.
"There are mistakes in similar areas. It is difficult to manage but yeah, it happens many times.
"Players take decisions in the moment, sometimes it works and sometimes it doesn't. We arrived in the last minute with the result but we could not keep it.
"It belongs to all of us, not just the players. I have not a problem to accept that it doesn't work like it worked in the past. It is all of us.
"They want it, how they run and how they do it but the truth is that we are not stable enough in the moments. At the end, today is what it is and after tomorrow we have to continue to learn.
"There are many, many good things that we played. The result is what it is. Of course we did many good things, things can improve and always give credit for the opponent and the quality they have."