Gittin Daf 19

The Gemara discusses a case if witnesses do not know how to sign their names for a Get - may we write their names in red dye, and they will write over this in black ink because regarding Shabbos, the top writing is considered writing? The Gemara answers no because of the concept of "V'chi mipnei she'anu medamin na'aseh ma'aseh" just because we suspect, or speculate, what the law is, should we rule that way in practice? The Gemara is telling us that we cannot use the same set of rules to determine when we should be lenient as in the case of Get and when we should be strict, as in the case of Shabbos. Often we set different rules for ourselves for ruchniyus and gashmiyus, like when to hit the snooze button because we need extra energy today.....would it be the same rule if we had to get up and be on time for shacharis or if we had a plane to catch ??