I would not categorize the first assault at Vicksburg on May 19th as being knowingly suicidal. Grant had achieved a series of open field victories against Pemberton's Army of Mississippi which led to that force withdrawing into its Vicksburg entrenchments. Grant authorized the first assault in the hope that it would lead to Vicksburg's fall and negate the necessity of a siege. Yes, that limited attempt failed but it prompted Grant to attempt a second assault on May 22nd. That assault was made along a longer front, and the portion of the assault at the Stockade Redan was in fact termed a "forlorn hope." The failure of the second assault ended any chance of quickly capturing Vicksburg, but convinced Grant that further direct attacks were futile. As far as Cold Harbor is concerned, a similar pattern presented itself. Grant had maneuvered Lee and the ANV from the Rappahannock almost to the James River, but was not successful in destroying the ANV. Cold Harbor was Grant's last chance to salvage the Overland Campaign and achieve a damaging blow to the enemy. Once again, that assault failed and Grant was forced to abandon his campaign, and alter his strategy by crossing the James and striking at Petersburg's underbelly. So although in retrospect, Grant regretted these assaults, his motivation for carrying them out at the time was based on calculated military reasoning. Right or wrong, Grant believed that he could achieve his goals by overcoming enemy forces in these cases. Let's remember that Grant was a highly aggressive commander, a trait that ultimately led the way to northern success. His use of direct assaults was still a limited tactic but one that he maintained in his toolbox.