Imagine if we defined price stability as zero percent inflation in the euro area. That would mean prices would be rising in some euro area countries, but falling in some other euro area countries. It would mean that as soon as some products became more expensive, the prices of others would have to fall. Otherwise you cannot achieve an average of zero.
Imagine if we defined price stability as one percent: that would mean we would have hardly any scope to reduce the interest rate and intervene if there was a downturn. Our margin of safety would then be too small. If you look at it from a long-term perspective, there are very good reasons to aim for close to two percent.