[quote="Zenkai, post:4, topic:331033"]
I thought that hiding something from a parent might be a mortal sin.
Yeah, well, if hiding something from parents is a mortal sin, then it's a mortal sin almost everyone has committed. Seriously. And it's because of the line "better to ask forgiveness than ask permission".
But, in all honesty, if you ask a priest if something is a mortal sin in confession, often times he will say something along the line of "it wasn't this time, but next time, it will be." In other words, if you don't really understand the seriousness of your own sin, it's not a mortal sin.
In order for a sin to be a mortal sin, it has to be something that is a serious matter, you have to have FULL KNOWLEDGE of the sin being a serious matter, and it must be done COMPLETELY willfully. As such, it's something that is very wrong; you know it is very wrong (and why it is wrong); and you did it anyway without being forced, being coerced into it, being addicted to a given sin, having an intellectual disability or a mental illness which prevents full control of the will, or being in a situation where the only choices are sinful choices (which is why lying to protect innocent Jews in WWII, though sinful, was not a mortal sin - the other choice was the betrayal of an innocent person to definite slavery and possible death, which is an even more serious sin), etc. Really, only God and the sinner know if the sin committed was mortal or not, which is why in confession, the priest becomes Jesus Himself when he absolves you (as he does when saying the words of consecration during the Eucharistic prayer). It is not the priest who absolves you of your sins, it is Jesus Himself.