When importing via Importacular, you do need to be aware of your Required Fields as well as Key Fields.
There are two types of Required fields. The first type includes fields required by Raiser’s Edge. These fields are required for all Raiser’s Edge users and include things such as a Last Name for an Individual record, an Organisation Name for an Organisation record and a Key Indicator. Additionally, your organisation may have made optional Raiser’s Edge fields required via Configuration. Regardless of whether or not a field is required for all users or just your organisation, if it is required, you must have a mapping for that field in your template (though you may want to use the field settings to set it to not update for existing constituents).
Key fields are often required, but not always. If a key field is left blank, then Importacular will not map that area. For example, a key field for a gift is the gift amount. Because the gift amount is also a required field, you have to map either a Source Field or a Default Value to map a gift in your template. However, if a row in your data source has a blank in the column that has been used to determine the gift amount, then that constituent will not have a gift populated. The fact that the amount is a required field was satisfied by the fact that a Source Field was selected, but since that row had a blank in it, a record was not created due to a blank key field.