אמר רבה בר בר חנה אמר ר’ יוחנן וקשין לזווגן כקריעת ים סוף
The Gemorah in Sota 2A says that a shidduch is like splitting the Yam Suf. Just like by Yam Suf klal yisroel did not see a solution, but Hashem did a totally unexpected miracle and all of a sudden they were saved. So too when people are trying to find a shidduch, they might be totally discouraged and not see a way out. But al of a sudden they meet the right person and they are engaged. Afterwards it seems so simple that the shidduch happened.
Likewise by the final redemption, it seems so long, the situation seems hopeless, but all of sudden Hashem will redeem us. Then we won’t understand how anybody could have doubted it.