First Thessalonians 4:13 says, "But we do not want you to be uninformed, brothers, about those who are asleep, that you may not grieve as others do who have no hope." Notice that the text does not say that we shouldn't grieve, just that we should grieve differently than those who have no hope.
Even in the context of hope, we still grieve, and that is appropriate. Jesus Himself wept at His friend's tomb. The Bible does not dismiss or minimize grief, and we shouldn't underestimate its impact. But we grieve differently than those without hope.