It raises an issue about the quality of this wizard: why on earth doesn't it read metadata for the target table and set lengths accordingly? It shouldn't be a permissions issue, because if I can write into a table I'd better be allowed to discover the column widths. So this wizard seems poorly thought out.
And don't get me started with the problems I've had where SQL Server reads metadata from a portion of my Excel or flat files when running an OPENROWSET query against them. The not infrequent result is a type conversion error or truncation issue further down the file.
Thankfully, IMEX=1 (Excel) and MaxScanRows=0 (flat files, more info. here) force SQL Server to scan the entire file. Then I can at least pull everything into a staging table and run data checks with T-SQL.